Luis Castillo Traded to White Sox as Mariners Get 3 Players, Full Trade Details

Starting pitcher Luis Castillo's time with the Seattle Mariners has come to an end after he was traded to the Chicago White Sox on Saturday, the team announced.

The Mariners will receive right-handed relief pitcher Seranthony Dominguez, outfielder Nolan Jones and catching prospect Boston Smith from the White Sox in exchange for Castillo.

ESPN's Jeff Passan first reported the deal, while Alden Gonzalez of ESPN provided a look at the financials:

There were rumblings prior to the 2025 season that the Mariners were at least exploring trade opportunities for Castillo.

MLB.com's Daniel Kramer noted in December 2024 the Mariners didn't necessarily want to trade Castillo, but ownership was only giving the front office roughly $15 million to $20 million to spend on the roster to make additions for the upcoming season.

It wound up being an extremely quiet offseason in Seattle, with Donovan Solano being the only free agent signed to an MLB contract.

After making a run to the ALCS for the first time in 24 years last season, it seemed like the Mariners would be more inclined to give this core another chance to show what they can do together.

This season has been a step back for the Mariners thus far, though they are only a few games behind the Houston Astros for the top spot in the AL West despite their 54-58 record.

Castillo is also on an affordable contract, though his 5.06 ERA and brief demotion from Seattle's rotation makes him less attractive. He is signed through 2027 with salaries of $24.2 million in each of the next three years, plus a $25 million vesting option that kicks in if he pitches at least 180 innings in 2027.

The Mariners were largely banking on their main core maintaining the level of play they were at in 2025. It hasn't panned out in part due to Cal Raleigh missing time with injuries and not repeating his MVP-caliber performance.

Even though losing Castillo does sting, the Mariners have built up a deep starting rotation that should be okay, especially if George Kirby and Bryce Miller return to form after injuries hindered their performance in 2025.

As for the White Sox, they are getting one of the best and most reliable starters in baseball for the next three seasons. Castillo has started at least 30 games in each of the past three seasons and ranks third in MLB in starts since 2018 (228).

A three-time All-Star, Castillo shook off a slow start in 2024 to finish with a 3.64 ERA in 175.1 innings. His new team will be counting on something similar this time around as they look to make a playoff push.